1. Field of the Invention
This invention relates to the isotope separation art and, more particularly, to a selectively photon-induced energy level transition of an isotopic molecule containing the isotope to be separated and a chemical reaction with a chemically reactive agent to provide a chemical compound containing atoms of the isotope desired.
2. Description of the Prior Art
In many applications, it is often desired to provide an isotopically concentrated element. That is, many elements exist in nature in several different isotopes and it is desired to isolate a single isotope to provide a substantially higher concentrate of the isotope than occurs naturally. One such application, of course, is providing a high concentration of the isotope U.sup.235. U.sup.235 constitutes only 0.7% of naturally occurring uranium. The balance of the uranium, 99.3% is U.sup.238.
Many different techniques have been proposed and/or utilized to provide the separation of the isotope U.sup.235 from naturally occurring uranium. Among these techniques have been gaseous diffusion through porous barrier materials, electromagnetic separation, centrifuging, thermal diffusion, chemical exchange and, more recently, ultra-centrifuge and jet nozzle techniques. Of these, the most widely used technique is the gaseous diffusion technique which, unfortunately, is relatively inefficient, comparatively expensive and requiring multiple passes of gaseous uranium through the barrier materials to obtain a high concentration of the U.sup.235.
Other isotopic separation techniques have been utilized for elements which have a low boiling point. For example, there has heretofore been proposed, in U.S. Pat. No. 2,713,025, an isotope separation technique applicable to mercury wherein a mercury vapor lamp, containing isotopically pure mercury, is utilized to irradiate a low-temperature vapor of naturally occurring mercury. The photons from the isotopically pure mercury vapor lamp excite only the same isotope atoms in the mercury vapor and cause photon-induced transitions between energy states thereof. At an excited energy state the mercury combines with water to form mercuric oxide. Since the photons were emitted from a single isotope of the mercury, only the same corresponding isotope in the mercury vapor was excited and thus isotopically pure mercury could be obtained from subsequent processing of the mercuric oxide. This technique, while applicable to some low boiling-point elements, cannot be readily adapted to the higher boiling-point isotopes such as uranium without severe penalties in process economics. The reason is that to provide a vapor of uranium would require comparatively high temperatures. To prevent excessive pressure broadening and Doppler broadening of the absorption/emission lines of the uranium atoms such that the absorption/emission lines of the U.sup.238 atoms substantially overlap the U.sup.235 atoms, expensive operations at pressures on the order of 10.sup.-2 Torrs and temperatures of 2000.degree. to 3000.degree. K are necessary. U.S. Pat. No. 3,673,406 merely shows an improvement to U.S. Pat. No. 2,713,025 but does not in any way indicate how the above shortcomings can be overcome.
Another technique heretofore proposed involving photoninduced transitions, as disclosed in U.S. Pat. No. 3,405,045, involves the irradiation of organic monomers with coherent radiation from a laser to effect a photo-disassociation of the monomer into free radicals. The free radicals then are utilized to initiate a polymer chain reaction, thus effecting the desired polymerization. Such teaching does not appear to be generally applicable to isotope separation.
Another technique, specifically designed for isotope separation of uranium hexafluoride (UF.sub.6) to obtain, ultimately, isotopically concentrated U.sup.235 F.sub.6, as disclosed in U.S. Pat. No. 3,443,087, involves irradiating a moving stream of UF.sub.6 with two separate beams of electromagnetic radiation. The first beam of electromagnetic radiation raises the internal energy of only the U.sup.235 F.sub.6 from the ground energy state to a higher, excited energy state. The second beam of electromagnetic radiation acts only upon the excited-state U.sup.235 F.sub.6 molecules and raises them past the ionization potential to provide ionized molecules of U.sup.235 F.sub.6. A magnetic field and/or an electric field are then applied to the ionized U.sup.235 F.sub.6 molecules to deflect them from the path of the unexcited U.sup.238 F.sub.6 molecules in an attempt to effect the separation. However, while the utilization of lasers to provide the photons has been suggested, no technique for selectively providing the photons in the first beam of electromagnetic radiation only with energies corresponding to the U.sup.235 F.sub.6 transitions, and not also to the U.sup.238 F.sub.6 transitions was actually proposed. Further, the partial utilization of electronic-excited and/or ionized states limits reaction times, since the decay time for electronic-excited and ionized states is quite short. Finally, and most importantly, there is considerable overlap of spectral lines of U.sup.235 F.sub.6 and U.sup.238 F.sub. 6 under practical operating conditions that allow significant ionization and/or electronic excitation in gaseous UF.sub.6 thereby rendering this isotope separation process rather inefficient.
In another isotope separation technique utilizing a hydrogen fluoride laser, as disclosed in "Isotope Separation with the CW Hydrogen Fluoride Laser," Applied Physics Letters, Vol. 17, No. 12, Dec. 15, 1970, separation of low mass molecules to effect a separation of deuterium from hydrogen is proposed. This technique involves the irradiation of a gas combination of methanol H.sub.3 COH, deutero-methanol D.sub.3 COD, and bromine Br.sub.2. The methanol is intended to be selectively reacted with the bromine, leaving the deuteromethanol in the gas phase. Deuterium is, of course, the desired isotope to be concentrated. Thus, the methanol absorbs the radiation from the hydrogen fluoride laser and reacts with the bromine. No filtering or fine tuning of the laser radiation is utilized since the absorption lines of the methanol H.sub.3 COH and the deutero-methanol D.sub.3 COD are very widely separated. High mass isotopes, on the other hand, have very closely spaced absorption lines that are virtually optically unresolvable except at very low temperatures and/or pressures. Consequently, direct unfiltered and/or untuned utilization of laser radiation to effect isotopic separation in high mass molecules is not practical.
U.S. Pat. No. 3,772,519 merely shows a separation technique for atoms utilizing lasers for preferential isotope excitations and subsequent ionization together with an electromagnetic separation.
German Patent No. 1,959,767 and British Patent No. 1,284,620 by Karl Gurs cite some general concepts of isotope-selective excitation of molecules in the vibrational and/or rotational modes, with a CO.sub.2 laser, and chemical reaction with an excited molecule. However, no new method or satisfactory technique is revealed in these patents beyond what was already known (see for example J. de Chim. Physique 60, 205 (1963)). No satisfactory structure is shown or described for providing an operable device by which the isotopes of uranium, for example, can be separated by incorporating a laser excitation of uranium hexafluoride. Further, the physical parameters and conditions set forth therein do not appear to be in the correct range for achieving the desired result. (See for example the report on Gurs' most recent attempts to effect the isotope separation of uranium hexafluoride as disclosed in a recent paper: "Uranium Isotope Separation Using IR Lasers" by H. Jetter and K. Gurs, Paper No. 4, International Conference on Uranium Isotope Separation, London, Mar. 5-7, 1975. The inventor reported that, utilizing Gurs' suggested techniques, no satisfactory separation could be achieved.
Thus, there has not heretofore been provided a completely satisfactory and economical photochemical technique for separating heavy isotopes and, in particular, for isotopic separation of desired U.sup.235 isotope from naturally occurring uranium.